Hydrogen gas is a clean, non-polluting fuel and chemical reagent, which is currently used in many industries. With the demand for hydrogen growing every year and the fact that hydrogen is explosive at only a four (4%) percent concentration in air, the ability to detect hydrogen gas leaks economically and with inherent safety is desirable and could facilitate commercial acceptance of hydrogen fuel in various applications. For example, hydrogen-fueled passenger vehicles will require hydrogen leak detectors to signal the activation of safety devices such as shutoff valves, ventilating fans, and alarms. In fact, such detectors will be required in several key locations within a vehicle—namely, wherever a leak could pose a safety hazard. Therefore, it is critically important to carefully measure, monitor, and strictly control hydrogen wherever and whenever it is used.
The real and perceived hazards of hydrogen fuel use, its production, and storage require extensive safety precautions. Local, state and federal codes must be put in place before any serious movement can be made towards a hydrogen based energy future. Currently, commercial hydrogen detectors are not practical for widespread use, particularly in transportation industry applications, because commercial detectors are too bulky, expensive, and dangerous.
There exist several hydrogen sensors having a palladium layer that is particularly attractive for transportation industry applications. These hydrogen sensors are termed Hydrogen Field Effect Transistors (HFET), thick film (e.g., incorporating a palladium alloy paste), thin film, and fiber optic. The HFET construction uses a thin film of Pd as the metal contact controlling the device. The presence of hydrogen results in the migration of atomic hydrogen to the interface between the metal film and the insulator, which results in a change in the output of the device that is scaled to the hydrogen concentration. The thick film device uses a thick film Pd alloy paste to form a four-resistor network (i.e., a Wheatstone bridge) on a ceramic substrate. The configuration is such that two opposed resistors result in a change in resistivity of the thick film material and a shift in the balance point of the bridge, which can be scaled to the hydrogen concentration. The thin film device is equivalent in design to the thick film, with only much thinner films (typically vacuum deposited) used as the resistors.
The fiber optic hydrogen sensor is a gasochromic-type (i.e., one that changes color when activated by hydrogen) sensor and is available in a variety of configurations with coatings, typically either palladium or platinum, at the end of an optical fiber that sense the presence of hydrogen in air. When the coating reacts with the hydrogen, the optical properties of the coating are changed. Light from a central electro-optic control unit is projected down the optical fiber where the light is either reflected from the sensor coating back to a central optical detector, or is transmitted to another fiber leading to the central optical detector. A change in the reflected or transmitted intensity indicates the presence of hydrogen. While the fiber optic detector offers inherent safety by removing the application of electrical power and by reducing signal-processing problems by minimizing electromagnetic interference, critical detector performance requirements (i.e., for all four configurations described above) include high selectivity, response speed, and durability as well as potential for low-cost fabrication. The optical senor is not necessarily limited to a fiber optic delivery system but may be included on any optical element.
Unfortunately, all of the conventional catalytic metal-based hydrogen sensors have the potential for degradation in their performance over time due to mechanisms that are inherent in their construction, a result of their cyclic interaction with hydrogen, or contamination from impurities in the environments in which they will be used. While various attempts have been made to protect the palladium or platinum catalytic surfaces, these attempts have not significantly improved sensor performance. Therefore, a need exists to limit degradation thereby allowing hydrogen sensors to operate over extended periods of time in the presence of contaminants.
Another application is in the proton electrolyte membrane (PEM) fuel cell. This fuel cell is an electrochemical device that produces electricity from a combined chemical reaction and electrical charge transport. The device uses a simple chemical process to combine hydrogen and oxygen into water, producing an electric current in the process. At the anode, hydrogen molecules are dissociated by a metallic catalyst (usually platinum) into hydrogen atoms, which eventually gives up electrons to form hydrogen ions. The electrons travel through an external circuit to produce usable electric energy while the hydrogen ions are transported internally to the cathode where they both combine with oxygen to form water. The platinum catalyst of the fuel cell anode is subject to degradation by contaminants similar to that of catalytic metal-based hydrogen sensors. Application of a protective coating to the surface of the anode of the platinum catalyst to prevent fouling and maintain the catalytic activity of hydrogen dissociation is advantageous to fuel cell performance.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawing.